JP2006019912A - Method for manufacturing surface acoustic wave element and photomask therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately transfer a (electrode) patterning printed on a photomask to a piezoelectric substrate wafer when an electrode pattern of a surface acoustic wave element is formed. <P>SOLUTION: The photomask used to form an electrode on the surface acoustic wave element arranged on the wafer constituting a surface acoustic wave device is provided with a gap where a main surface of the piezoelectric substrate and the photomask come into contact with each other to improve evacuation of the gap between the piezoelectric substrate and the photomask. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to the formation of an electrode of a surface acoustic wave element constituting, for example, a surface acoustic wave device.

  Recent mobile communication devices and mobile phones are increasingly required to have advanced structures and specifications in terms of form and function. Regarding the surface acoustic wave device used for this, the surface acoustic wave device itself is downsized and Correspondence to forms such as low profile and filter specifications that are small but not different from conventional ones are desired. More recently, there is a demand for high-density communication lines with a large number of communication lines, and there is an urgent need for advanced specifications for the filter function of functional parts that accurately divide transmission and reception frequencies for transmitting call signals. Yes.

  Regarding the above-described filtering of transmitted / received signals, a surface acoustic wave device as a bandpass filter using surface acoustic waves is used in the field of mobile communication and the like. Surface acoustic wave devices in such fields are required to have extremely high-performance band characteristics, in particular, to have attenuation characteristics that greatly attenuate outside the band, and are stable in order to reduce the unit price of the product. There is also a need for an environment that enables mass production.

The surface acoustic wave element, which is the main component incorporated in the surface acoustic wave device, propagates the bulk wave on the surface of the piezoelectric substrate and realizes filtering characteristics. Therefore, the electrode material formed on the piezoelectric substrate is generally made of aluminum or the like. A light metal is used, and one of the electrode forming methods is to provide a resist on the surface of the piezoelectric substrate, then provide a photomask on the surface of the piezoelectric substrate, expose the surface resist, and perform an etching process. Electrodes are formed on the main surface and the surface of the piezoelectric substrate using a photolithographic method.
Japanese Patent Laid-Open No. 2003-110389

  A part of the electrode formation process described above is a process in which the photomask and the piezoelectric substrate are brought into close contact with each other and exposed (UV: irradiated with ultraviolet rays) in the manufacturing process using the photoresist and the photomask as described above. Has been taken. When exposing an electrode pattern with a general photomask and a piezoelectric substrate in close contact with each other, the electrode pattern of the surface acoustic wave element printed on the photomask is accurately obtained as a piezoelectric substrate (an electrode as a surface acoustic wave element is obtained). It is desirable to improve the close contact between a photomask and a wafer on which a plurality of surface acoustic wave elements are arranged. For this purpose, a manufacturing process has been introduced in which the contact surface between the mask and the woofer is in a vacuum state and the degree of contact is increased by increasing the degree of vacuum during contact.

  However, when the photomask and the piezoelectric substrate are brought into close contact, the adhesion between the photomask and the piezoelectric substrate (non-adhesiveness) is caused by the problem of warpage of the wafer itself and the difference in thermal expansion coefficient between the photomask and the piezoelectric substrate. Since the adhesiveness varies due to the influence of sufficient undulation), interference fringes may occur when the adhesiveness is not uniform on one wafer when UV is irradiated. For this reason, variations occur in the transfer accuracy of the electrode pattern, and there arises a problem that the electrical characteristics and the in-wafer in-plane frequency vary.

  Therefore, in order to solve the above-described problems, in a photomask used for forming electrodes on a surface acoustic wave element disposed on a wafer constituting a surface acoustic wave device, the main surface of the piezoelectric substrate and the photomask are A photomask characterized in that a vacuum is drawn between the piezoelectric substrate and the photomask by leaving a space between the main surface of the piezoelectric substrate and the photomask in a state of being in close contact with each other.

  In short, when the photomask and the piezoelectric substrate are brought into close contact with each other, the adhesion between the photomask and the piezoelectric substrate (adhesion failure) due to the problem of warpage of the wafer itself and the difference in thermal expansion coefficient between the photomask and the piezoelectric substrate. Adhesion varies due to the influence of sufficient waviness). Therefore, a plurality of grooves are formed between the photomask patterns on the surface in contact with the photomask, or the photomask on the surface in contact with the photomask. By increasing the patterning thickness to form the pattern by 1.5 to 2.0 times, the electrode pattern of the surface acoustic wave element printed on the photomask is accurately obtained from the piezoelectric substrate (the electrode as the surface acoustic wave element is obtained). Conventionally, by increasing the effect of evacuation to improve the adhesion between the photomask and the surface acoustic wave element used in the process for transferring To solve the problems.

  As described above, the present invention increases the adhesion between the piezoelectric substrate and the photomask, thereby improving the adhesion when the resist film is subjected to the exposure process, so that one electrode pattern printed on the photomask can be obtained. By transferring to a plurality of electrode patterns as surface acoustic wave elements arranged on a piezoelectric substrate wafer, variation in electrical characteristics within one wafer surface can be reduced, and the in-plane frequency distribution can be stabilized. it can. As a result, by improving the yield in the manufacturing process and increasing the production quantity per unit time, the manufacturing unit price can be reduced and the quality can be maintained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In each figure, the same numerals indicate the same objects. In the description of the embodiments, the electrode pattern is conceptually expressed, but the actual electrode pattern is a substitute for the comb-shaped excitation electrode or the reflector electrode of the surface acoustic wave element. Moreover, although described as an embodiment in which the electrode is formed by etching, the same function and effect are exhibited even when the lift-off method is used in forming the electrode.

  In the present invention, a resist film 8 is provided on the surface of the piezoelectric substrate, a photomask 4 is in close contact with the surface of the piezoelectric substrate, the resist film 8 is exposed, and then an electrode film is formed on the surface of the piezoelectric substrate. Next, the photomask 4 used in the electrode pattern 3 process of the surface acoustic wave element 2 for removing the resist film 8 on the surface is characterized.

  FIG. 1 shows a piezoelectric substrate 1 made of quartz, lithium tetraborate, lithium tantalate, lithium niobate or the like having a thickness of 300 to 500 μm, and an electrode pattern is arranged on the surface side (main surface side) of the piezoelectric substrate 1. In addition, an aluminum material having a thickness of 0.05 to 1.5 μm is applied to the surface on which the surface acoustic wave is propagated, and a resist film 8 made of an organic polymer having a thickness of 0.1 to 2.0 μm is provided thereon. ing. In this state, a photomask 4 in which a light-shielding film made of chromium or the like is patterned 11 is placed on the piezoelectric substrate 1 in close contact with the piezoelectric substrate 1 on the surface of the piezoelectric substrate 1 such as quartz glass (SiO 2).

  Then, light (UV: ultraviolet) is irradiated through the opening 7 of the photomask 4 and thereafter development processing is performed. As a result, a resist pattern recess 9 having the same shape as the opening 7 of the photomask 4 is formed on the surface of the piezoelectric substrate 1 as shown in FIG.

  Here, the photomask 4 which is a feature of the present invention will be described. The electrode pattern 3 of the surface acoustic wave element 2 arranged on the wafer 1 of the piezoelectric substrate is formed by the above-described process. At this time, it is necessary to irradiate UV with the photomask 4 and the wafer 1 in close contact with each other. However, the photomask 4 has a thickness of 2.3 μm in consideration of the warpage of the photomask 4 and may lack adhesion due to minor differences in thermal expansion from the piezoelectric substrate.

  Therefore, as shown in an enlarged perspective view of a part of the photomask 4 shown in FIG. 3, a photomask 4 structure that improves the adhesion by bringing the photomask 4 and the piezoelectric substrate into a vacuum state has been considered. FIG. 3A is a partial cross-sectional view showing a state in which the photomask 4 side between the electrodes is scraped to be formed in the surface acoustic wave element 2. FIG. 3B is a cross-sectional view showing a state where the thickness of the patterning 11 is increased when the light shielding film made of chromium or the like is patterned 11.

  FIG. 4 is a view assuming that the photomask 4 shown in FIGS. 3A and 3B is used and the piezoelectric substrate is brought into close contact with each other to be in a vacuum state. In addition, since a gap can be secured compared with the conventional mask, the patterning accuracy can be improved by improving the evacuation effect in the vacuuming step. Here, the gap between the photomask and the piezoelectric substrate before the vacuum state is 1000 mm. A major feature of the present invention is that it is always warped when patterning a piezoelectric substrate. In the conventional process, a vacuum pressure sufficient to forcibly correct the warp cannot be obtained with a photomask. Therefore, in the present invention, a sufficient gap is secured between the photomask and the piezoelectric substrate, so that the photomask and the piezoelectric substrate are secured. A vacuum pressure between the substrate and the substrate can be ensured, and patterning for the piezoelectric substrate can be processed uniformly.

  By using the photomask 4 on which the groove 5 of the present invention is formed, the adhesiveness with the wafer 1 is improved, so that physical factors such as warpage, swell, or difference in thermal expansion coefficient between close objects. As for the surface acoustic wave element 2 arranged on the wafer 1, the transfer accuracy of the electrode pattern 3 is improved, so that variation in electrical characteristics within the same wafer 1 surface is obtained. And the in-plane frequency distribution can be stabilized. The in-plane frequency distribution is shown in FIG.

  FIG. 5 is a graph in which the horizontal axis indicates the variation amount of the normalized frequency and the vertical axis indicates the dispersion amount of each frequency. FIG. 5A is a frequency distribution obtained by using the photomask 4 of the present invention. (B) is a frequency distribution obtained using the conventional photomask 4. As can be seen from the figure, since the variation in frequency is distributed to the center according to the present invention, the positional (local) electrode pattern 3 of the surface acoustic wave element 2 formed on one wafer 1 is transferred. It can be seen that the variation is improved. The good or bad in this step is that when the actual surface acoustic wave device is formed, the ripple in the pass band and the variation in the pass band width can be improved.

It is sectional drawing explaining the concept which forms an electrode pattern. It is sectional drawing which shows the concept of the surface acoustic wave element after forming an electrode pattern. It is the perspective view which expanded a part of photomask which gave the groove part of this invention, and showed the concept. It is sectional drawing which shows the state which contact | adhered the photomask and the piezoelectric substrate in the vacuum state by this invention. It is a graph which shows the change of the electrical property variation of a surface acoustic wave element in a wafer plane.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wafer 2 Surface acoustic wave element 3 Electrode pattern 4 Photomask 5 Groove part

Claims (2)

In a method for manufacturing a surface acoustic wave element, an electrode is formed using a photomask on a surface acoustic wave element disposed on a wafer constituting the surface acoustic wave device.
A space is provided between the main surface of the piezoelectric substrate and the photomask in a state where the main surface of the piezoelectric substrate and the photomask are in close contact with each other, and the air between the piezoelectric substrate and the photomask is evacuated. A method for manufacturing a surface acoustic wave device. In a photomask used for forming an electrode on a surface acoustic wave element disposed on a wafer constituting a surface acoustic wave device,
In order to ensure a close contact between the main surface of the piezoelectric substrate and the photomask with a gap between the main surface of the piezoelectric substrate and the photomask in a state where the main surface of the piezoelectric substrate and the photomask are in close contact with each other A photomask comprising a plurality of grooves formed between photomask patterns arranged on the photomask.

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